Yabbies are tasty, but they are only one of 38 freshwater crayfish species in Victoria.avlxyz/Flickr

Someone who recently discovered that I do research on freshwater crayfish asked a simple question: How long do yabbies live? But this simple question has no simple answer. I found myself opening and closing my mouth as I tried to figure out where to start, and realised I looked like a complete idiot.

Why is this such a hard question to answer?

Well, it depends on a bunch of stuff. It depends on the yabby, for starters. What species of yabby does the questioner have in mind? It depends on the habitat. Is the yabby in a dam, a river, underground in a burrow or in a fish tank in your bedroom? It depends on the environment and the weather. Is there a drought or a recent flood? Has a bushfire filled the river with ash?

And it depends on the luck of the yabby. Most yabbies die young, because they are on everyone’s menu. If they are not eaten by a fish or a bird or another yabby, they are likely to end up on your plate.

Indeed, when I put “yabby definition” into my search engine to find out what other people mean when they say the word yabby, I got the following: “A small freshwater crustacean with a sweet, delicate flesh. Yabbies can be substituted with shrimp or crawfish.” In other words, when most people think of yabbies, they are thinking of food.

To me, however, yabbies are members of the genus Cherax, a group of freshwater crayfish found almost exclusively in Australia. More specifically, it usually refers to the species Cherax destructor, which is also known as the common yabby.

Last week, in the state of Victoria, the government changed the rules about catching yabbies. They have set the bag limit to 200 individual yabbies per day, which is in line with the rules in New South Wales and South Australia. Previously, the limit was 30 litres, and the problem was that if people were chasing juvenile yabbies for the purpose of selling them as bait, they could collect literally thousands of yabbies every day. If kept up for an extended period, this fishing practice could destroy entire populations.

Another change to the yabby rules is that berried females must now be returned to the water. A female in berry is carrying eggs under her tail, so that killing her would result in the unnecessary death of hundreds of unhatched yabbies. All other freshwater crayfish are protected in this way, and it is common sense to provide this minimum protection, even for a species known as C. destructor.

The final change provides a little relief for the yabby hunter: a new type of net has been approved for catching yabbies. The old opera house net is banned in public waters in Victoria and eastern New South Wales because of the risk of catching platypus, water rats and turtles, who will drown if caught in these nets. The new open-top pyramid nets allow the fisher to set a trap that will hold a reasonable haul of yabbies, while allowing protected air-breathing species to escape.

There are well over a hundred species of freshwater crayfish throughout Australia, and some people call them all yabbies. Most people can recognise the really tasty versions: marron, red claw and crays, but all of these are hard to tell apart when they are still small. Unfortunately, people sometimes use juvenile Murray crays as bait because they assume that any small crayfish are yabbies. Being able to tell the species apart would really help with their conservation.

There are 38 species of freshwater crayfish in Victoria, of which 27 species are threatened. Freshwater crayfish are critical components of ecosystems where they are found: as juveniles they are tasty snacks for other species, and as adults they are top predators critical to managing the food web. Crayfish are environmental engineers – they dig burrows, chew on submerged logs and rearrange aquatic vegetation, all to the benefit of other freshwater species. If the crayfish are removed from the system, our freshwater systems will suffer.

So how long can a yabby live? In a farm dam, with a good source of food and a bit of luck, they could live for ten years, although five years would be more common. But if the lake they are living in dries up due to drought, then the yabbies burrow down into the mud and aestivate (or hibernate), waiting for the next heavy rains. It is anyone’s guess as to how long they can stay down there.

Lakes that have been completely dry for many years become full of large yabbies within days of filling up with water. Those animals come out in such vast numbers, that these populations are enthusiastically targeted by fishers keen to harvest the bounty. Last year, a flood produced so many yabbies that the locals were scooping them up with shovels.

The problem is that these adults are a remnant population; their job is to feed and breed in order to produce the next generation of crayfish. When the droughts are long, and the fishing pressure is heavy, we risk removing the breeding stock and reducing the overall size of yabbies.

A bumper year is predicted for yabby harvests throughout south eastern Australia. This is a good time to remind ourselves that even the hardy, virtually indestructible species C. destructor needs to be protected from unrestrained fishing pressure.

How long can a yabby species survive? This is a hard question to answer, but the common yabby will remain common a lot longer under the altered fishing rules in Victoria.